1. Field of the Invention
The present invention pertains to the aiming of equipment producing radiant beams.
2. Background
Radiography is a technique for producing an image of an opaque object by transmitting radiation, such as an x-ray or gamma-ray beam, through the target object onto adjacent radiographic film. In addition to medical applications, radiography has been used to inspect the internal characteristics of objects in nondestructive inspection procedures. Radiographic imaging is used to identify internal damage, flaws and material anomalies without destroying the object inspected. Radiographic inspection is used in many industrial applications including, for example, production and testing of pipelines and boilers, production and inspection of nuclear equipment, shipbuilding and maintenance, aviation and aerospace, electrical engineering and electronics production and maintenance, metal casting, and automotive applications. Radiographic inspection is described in Cumings U.S. Pat. No. 5,402,577, which is incorporated herein by reference in its entirety.
The usefulness of a radiographic image often depends on the angle and direction at which the radiant beam strikes the target object to be inspected. For example, it is often desirable to produce a radiographic image of an object that shows an internal void between parallel structural members or materials (such as a honeycomb core). Such an image can be produced only if the radiant beam strikes the surface of the target object at an angle and direction that allows the radiation to pass through the internal void of the target object. Internal structural members, such as structural members forming a honeycomb core, frequently do not form a perpendicular angle with respect to the surface skin of a part. Hence, aiming a radiographic transmission machine so that the radiant beam strikes the surface skin of the target object at a perpendicular angle will not always produce a radiographic image allowing for adequate inspection of the interior void between internal structural members. To produce a radiographic image allowing inspection of the interior void of such a target object, the radiographic transmission device must be aimed so that the central ray of the transmitted beam strikes the surface of the target object, and passes through the target object, at a direction and angle substantially the same as the angle and direction that the interior structural member forms with the interior wall of the part. Directing the radiographic beam at such an angle and direction allows the beam to pass through the internal void of the part without passing through any structural members. This is just an example of the need for alignment of a radiant beam. Of course, objects having irregular shaped interior structures, or interior structural members which do not abut against the interior wall of the target object, may also require special alignment of the radiant beam for proper radiographic inspection.
Transmission systems typically used for the radiographic inspection allow the operator to aim the beam so that the beam can be passed through the target object at a desired direction and angle. One type of transmission system, an x-ray system, generally comprises an x-ray tube having a lens from which the x-ray beam is emitted. The tube is sometimes mounted to either a portable or stationary tube stand and is attached to a controller through which the operator can control and manipulate the position (angle) and orientation (direction) of the transmission source. For inspection of large parts, the part typically remains stationary and the x-ray lens is manipulated to aim the x-ray beam at the part to be inspected.
Because radiant beams are often invisible, the operator ordinarily must use some visible means to ascertain the angle and location at which the radiant beam will pass through the target object to be inspected. For example, in older x-ray systems, the x-ray beam was aimed through the use of a mechanical rod, which was extended between the desired location on the part to be inspected to the center of the x-ray lens. In this manner, the mechanical rod provided a visual representation of the angle, direction and location that the central ray of the x-ray beam would pass through the target object to be inspected. Such mechanical aiming systems are cumbersome and inaccurate, and have generally been replaced with laser light aiming devices, which are now commonly used for positioning various types of radiographic equipment. For example, prior use of a laser beam for orienting and aiming of an x-ray machine for medical applications is described in Cramer et al. U.S. Pat. No. 5,661,775 and Williams et al. U.S. Pat. No. 5,537,453. Prior art laser aiming devices generally operate under the same principle as prior art mechanical aiming devices. Generally, laser aiming devices have heretofore directed a visible laser beam coaxial with the central ray of the x-ray beam, giving a visual indication of the point at which the central ray will strike and pass through the target object.
One shortcoming of prior art laser aiming systems is that, while they generally provide an indication of the location that the central ray of the beam will strike the target object to be inspected, they do not provide an accurate visual indication of the angle and direction at which the beam will strike and pass through the target object. Until now, x-ray operators using conventional laser aiming devices have had no alternative but to use trial and error in order to seek to properly angle and direct the beam with respect to the target object to be inspected. Through the repetitive trial and error process, the x-ray operator aligns the x-ray machine using the laser, and then energizes the x-ray machine to produce an image on radiographic film. The operator then inspects the image to determine if the image was taken at the desired angle. If not, the operator then must adjust the angle of the x-ray lens and retake the image. This iterative process must be repeated until the operator produces an acceptable image at the desired angle and direction. This trial and error method is extremely expensive, time consuming and may result in poor quality inspections.
In many instances the desired angle at which the radiant beam should strike and pass through the outer surface of the target object can be predetermined. Thus, there is a substantial need for a method, system and apparatus, that will allow a radiant beam emitter to be aimed at a target object such that the radiant beam strikes the surface of the target object at the predetermined angle and direction. Such a method, system and apparatus will, among other advantages, eliminate the substantial time and expense associated with trial and error methods heretofore used with conventional laser aiming devices.